Alongside Leonardo DiCaprio and Brad Pitt in 'Once Upon a Time in Hollywood'.

The already stacked cast list for Tarantino's movie about the Manson murders just got a little more crowded. On Tuesday, Margot Robbie announced that she will star in Once Upon a Time in Hollywood, finally confirming the long-standing rumor that she will be playing Sharon Tate—the pregnant starlet and wife of Roman Polanski who was brutally murdered by Manson's followers in 1969 inside her Cielo Drive home, Deadline reports.

"Tarantino is one of my bucket-list directors," the actress told IndieWire earlier this week. "As long as I can remember, I’ve been a huge Tarantino fan." As for the idea of tackling the role of Tate, Robbie said she feels "a responsibility with every character I play, whether they’re fictional or real life to play her right, play her truthfully, and kind of understand her emotional journey."

Robbie is the third major star to sign onto Tarantino's ninth film alongside Leonardo DiCaprio and Brad Pitt, who will be playing Rick Dalton, a former Western star and Tate's next-door neighbor, and his stunt double, Cliff Booth, respectively. But it looks like there will be some major additions to the cast coming soon, too.

According to Deadline, Tarantino is eyeing Burt Reynolds for the role of George Spahn, the aging, blind owner of Spahn Ranch. Spahn Ranch was a defunct Western set where Manson set up his commune, reportedly keeping Spahn happy with sex from his young, female followers, and seeing as how DiCaprio and Pitt's characters are out-of-work Western actors, the Spahn connection seems only natural.

Other Tarantino standbys Tim Roth and Michael Madsen are apparently eyeing roles, as well, along with Kurt Russell, who previously starred in Hateful Eight and Tarantino's Grindhouse movie, Death Proof, but it's not yet known who they'll be playing.

None of them seem particularly well-suited to play Manson, though, so maybe Tarantino's planning to just pull a Pulp Fiction suitcase on us again and never actually give us a glimpse of Charlie himself. We'll find out for sure next year, when Once Upon a Time in Hollywood hits theaters August 9, 2019.